Lizards and Snakes: Alive!

By Edward Castillo

The following story is contributed by the Houston Museum of Natural Science, one of Natural History magazine’s Museum Partners. Members of any of our partner organizations receive Natural History as a benefit of their museum membership. Founded in 1909 to “enhance in individuals the knowledge and delight in natural science and related subjects,” the Houston Museum of Natural Science carries out that mission in every project, program, and exhibition. The Museum houses the Burke Baker Planetarium, Wortham IMAX® Theatre, Cockrell Butterfly Center, and more than a dozen permanent exhibit areas that examine astronomy, space science, Native Americans, paleontology, energy, chemistry, gems and minerals, seashells, Texas wildlife, and more. The Museum presents traveling exhibitions as well, one of which, “Lizards and Snakes: Alive!” featured more than sixty live snakes and lizards. The Museum also maintains two satellite facilities near Houston: The George Observatory in Fort Bend County, which houses one of the largest telescopes in the country that is available for public viewing; and The Woodlands Xploration Station, in Montgomery County, which has exhibits on dinosaurs, mineralogy, live insects, and more.

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Common leaf-tailed gecko

Emerald tree boa

Gila monster

Veiled chameleon

Rhinoceros iguana

D. Finnan/AMNH

While lecturing on the physiology of squamates (lizards and snakes) to a visiting group of students, the seven-foot boa constrictor I was holding adeptly demonstrated the recurved teeth it uses to grasp its prey.

As six rows of needle-like teeth pierced the skin of my forearm, I couldn’t help but appreciate the power, speed and efficiency of a snake bite.

Fortunately for me, the snake was more annoyed than hungry. As the students excitedly asked question after question, it was apparent that this was a small price to pay to instill appreciation and respect for this ancient group of reptiles.

The order Squamata, or scaled reptiles, includes over 7,000 species of lizards and snakes, making them an even more diverse group than mammals. Surviving for 200 million years, they are some of the most successful vertebrates on Earth, occupying important biological niches in all but the coldest environments. Both revered and despised by humans across the planet, few animal groups elicit such strong human emotions as these remarkable creatures. Lizards and snakes share many characteristics with their reptilian brethren—the turtles and tortoises, the crocodilians, and the tuatara. All are vertebrate lung breathers from birth. They are “ectothermic,” obtaining their body heat from the surrounding environment, and they possess keratinous scales derived from an outgrowth or thickening of the epidermis. Most produce amniotic or fluid-filled eggs that resist desiccation on land.

One adaptation that truly sets squamates apart from other reptiles is a highly specialized hinge in their jaw. Rather than hinging on a single point like the jaws of their primitive ancestors, the flexible jaws of squamates hinge from multiple points to allow for greater manipulation of prey and a faster, more powerful bite. This evolutionary marvel allows a gecko to efficiently chomp insects and a python to swallow a pig whole. With its 2 ¼ inch fangs, the venomous Gabon viper, Bitis gabonica, has no problem shifting each jaw independently to work its food further down its throat. Lizards and snakes easily disappear into their environment using a host of amazing skin patterns and textures. Leaf-tailed geckos, Uroplatus sp., are true masters of camouflage, using skin flaps and frills to disguise the outline of their body and a leaf-shaped tail to convince predators that their body is just another part of the landscape.

Using a different tactic, the frilled lizard, Chlamydosaurus kingii, faces its predators head-on. By extending the greatly exaggerated skin flap around the edge of its head, it gives an intimidating display to ward off even the most persistent predators. Other squamates advertise their presence by the use of aposematism (warning coloration), such as highly venomous coral snakes. The red, yellow and black coloration on these snakes is a warning that is hard to miss. The incredible chameleons use specialized skin cells called chromatophores to flash a variety of colors and patterns. These specialized pigment cells are located just beneath the outer layer of the skin surface and can be expanded and contracted as needed. These walking “neon signs” change colors based on mood, temperature and lighting. A male chameleon will also use its coloration to threaten other males and impress females. Among many impressive adaptations, the visual acuity of chameleons is most notable. The veiled chameleon, Chamaeleo calyptratus, of Yemen and Saudi Arabia uses its turreted eyes to see predators and prey on both sides of its body at the same time. Once the prey is located, both eyes work together, using binocular vision to accurately judge distance before the lizard explosively launches its long, sticky tongue to capture tonight’s dinner.

While the chameleon may use its tongue for grabbing prey, other squamates use their tongue for capturing scents. The long forked tongue of a Gila monster, Heloderma suspectum, captures scent particles both in the air and on the ground, and then transfers them to a specialized scent organ, located in the roof of the mouth. Once the prey is located, the Gila monster seizes it with a vise-like grip, subdues it using powerful venom, and then swallows it whole. The venom glands of squamates produce a wide array of toxic proteins capable of very interesting, yet devastating results. Some toxic components of squamate venom are highly necrotic, resulting in quick tissue digestion and hemorrhaging. Others result in a loss of blood pressure and clotting ability, even respiratory paralysis. The most dangerous snake in North America, the western diamondback rattlesnake, Crotalus atrox, can easily deliver a fatal bite using its long, hollow fangs. While hunting warm-blooded mammals, this snake employs a pair of heat-sensing pits located behind each nostril that are so accurate, they can detect even a slight change in temperature from over six feet away. However, evolution also works in favor of prey animals. In the never-ending arms race between predator and prey, some mammals, including the opossum, have evolved resistance to the powerful venom of this pit viper.

The red spitting cobra, Naja pallida, has an intimidating presence when it flattens its upper ribs to extend its characteristic hood. Its name is misleading, as the snake does not spit but rather squeezes the venom up from its glands and out through specialized fangs. While the venom is not particularly deadly when in contact with the skin, a direct injection of venom into the bloodstream from a bite can be fatal. Most often, spitting cobras keep their distance from predators, preferring to flee or spray an attacker in the eyes, which will result in permanent blindness. From their humble beginnings in the Jurassic period to their speciation on almost every continent on Earth, the history of squamates is a true success story. Mastering environments as varied as harsh deserts, lush rainforests and tropical oceans they have flourished while filling important ecological niches.